1. Field of Invention
The present invention relates to a semiconductor device, and more particularly to a lateral double diffused metal oxide semiconductor (LDMOS) device for an electrostatic discharge (ESD) protection circuit.
2. Description of Related Art
ESD is a phenomenon of electrostatic motion along a nonconductive surface. Semiconductor devices and circuits in ICs can be damaged by ESD. For example, a charge carrying object, such as a human body walking on a carpet, a machine for packaging ICs or an apparatus for testing ICs, can discharge to the IC chip when they are in contact with each other. Thus, the IC chip is damaged or broken by the transient power of ESD.
Therefore, a number of methods have been developed to protect semiconductor integrated circuit devices against possible ESD damages. The most common type of ESD protection is the incorporation of a special hardware inside the package. In other words, a specially designed ESD protection circuit is set up between an internal device and each bonding pad, so as to protect the internal device.
Currently, a lateral double diffused N-type metal oxide semiconductor (LDNMOS) device is an electronic device widely applied in the power management. When the internal device is a high voltage device such as a large-sized output driver, the output driver is coupled to a control circuit, and a gate-grounded LDNMOS device is used as an ESD protection device. However, the gate electrode of the output driver is floating under the ESD transient condition, so that the trigger voltage of the output driver is equal to, or even less than, that of the ESD protection device (i.e. gate-grounded LDNMOS device). Thus, the output driver might be turned on more quickly than the LDNMOS device for an ESD protection circuit (ESD LDNMOS device); hence, the ESD LDNMOS device is useless in protecting the output driver.
Accordingly, it has become one of the main topics in the industry to design an ESD LDNMOS device which can be turned on more quickly than the internal device.